Lubricating oil compositions

ABSTRACT

The present invention relates to a method of lubricating a passenger car motor vehicle engine having a rotating tappet, comprising lubricating the engine with a lubricating oil composition having up to 0.09 wt % phosphorus, 0.4 wt % sulphur and 1.0 wt % sulphated ash, and being substantially free of friction-modifier.

The present invention relates to passenger car motor vehicle lubricatingoil compositions. In particular, although not exclusively, the presentinvention relates to passenger car motor vehicle lubricating oilcompositions which exhibit improved wear performance.

BACKGROUND OF THE INVENTION

Lubricating oil compositions used to lubricate internal combustionengines comprise a base oil of lubricating viscosity, or a mixture ofsuch oils, and additives used to improve the performance characteristicsof the oil. For example, additives are used to improve detergency, toreduce engine wear, to provide stability against oxidation, to reducefriction loss, to increase fuel economy and to inhibit corrosion. Someadditives provide multiple benefits, such as dispersant-viscositymodifiers. Other additives, whilst improving one characteristic of thelubricating oil, are detrimental to another characteristic.

It has long been know to use friction modifiers, such asmolybdenum-containing compounds, and/or organic friction modifiers, suchas glycerol mono-oleate, in passenger car motor vehicles to reducefriction between moving engine parts and to improve fuel economy.

For example, U.S. Pat. Nos. 4,164,473 and 4,479,883, EP Patent No. 13469 and UK Patent No. 2 068 380 disclose various oil-soluble molybdenumcontaining compounds suitable as friction reducing additives for use inpassenger car motor vehicles. U.S. Pat. No. 6,723,685 discloses acomposition comprising a molybdenum additive and an organic frictionmodifier, in an amount sufficient to pass a Sequence VIB fuel economytest.

In addition, International patent application number WO-A-03/064568discloses use of friction modifiers as additives in lubricating oilcompositions to reduce wear in internal combustion engines.

In addition, as the permitted levels of sulphated ash, phosphorus andsulphur (SAPS) emissions from passenger car motor vehicles decrease thelevels of additives such as metal dialkyldithiophosphates that can beused are decreased. This leads to an inbalance in the additivecombinations conventionally used in passenger car motor vehicles andleads the formulator to consider new additive combinations in order tomeet the requirements of vehicle manufacturers.

Passenger car motor vehicle internal combustion engines have manydifferent conformations that have different lubrication requirements.One problem associated with lower SAPS lubricants is increased enginewear due to reduced phosphorus levels limiting the amount ofconventional anti-wear additives that can be used. This problem isparticularly evident for rotating tappets in the valve train, which canstall when lubricated with lower SAPS lubricants and exhibitunacceptable wear.

US 2003/0148895 A discloses lubricating oil compositions intended toreduce wear in the Peugeot TU3M Scuffing Test. This test is intended toinvestigate wear on the cam and tappets of an internal combustionengine. The disclosures of this document show that relatively highlevels of boron (derived from borated dispersant) and preferablyaugmented with significant amount of molybdenum (derived from, e.g., atrinuclear molybdenum additive) are required to reduce cam and tappetwear to acceptable levels.

WO 03/064568 A2 discloses lubricating oil compositions for use with lowsulfur fuels in internal combustion engines. The lubricating oils, whentested in a Sequence IVA test, result in increased wear (cam nose wearand total wear) as the molybdenum and boron concentrations thereof arereduced. Other disadvantageous effects are also apparent.

Preferred embodiments of the present invention seek to provide a methodof lubricating an engine comprising a rotating tappet to provideimproved wear performance, particularly in lower SAPS formulations.

SUMMARY OF THE INVENTION

The present invention provides a method of lubricating an internalcombustion engine having a cam and a rotating tappet associated with thesaid cam, the said method being defined by claim 1 of the set of claimsfollowing the description of the invention. Preferred and optionalfeatures of the invention are the subjects of the claims which aredirectly or indirectly appended to claim 1.

The present invention, in another aspect, provides a combinationcomprising an internal combustion engine having a rotating tappet and alubricating composition, wherein the lubricating composition has thecharacteristics specified for the lubricating composition of claim 1.

In yet another aspect, the invention provides the use of a lubricatingoil composition to pass the 650 hour Volkswagen (trade mark) RNT test(PV1473 Draft), and optionally the VW (trade mark) PV1451 FE test,wherein the said lubricating oil composition has the formulationspecified for the lubricating oil of claim 1, and optionally, one ormore of the features of the claims which are appended, directly and/orindirectly, to claim 1.

The present invention provides in a first further aspect, a method oflubricating a passenger car motor vehicle engine having a rotatingtappet, by lubricating the engine with a lubricating oil compositionhaving up to 0.09 wt % phosphorus, 0.4 wt % of sulphur and 1.0 wt %sulphated ash, based on the total weight of the composition, thelubricating oil composition comprising an oil of lubricating viscosityand being substantially free of friction-modifier.

In a second further aspect, the present invention provides a method ofreducing wear in a passenger car motor vehicle engine having a rotatingtappet, comprising lubricating the engine with a lubricating oilcomposition having up to 0.09 wt % phosphorus, 0.4 wt % of sulphur and1.0 wt % sulphated ash, based on the total weight of the composition,comprising an oil of lubricating viscosity and being substantially freeof friction-modifier.

In a third further aspect, the present invention provides a method ofreducing wear and in an engine having a rotating tappet whilstmaintaining fuel economy performance, comprising lubricating the enginewith a lubricating oil composition having up to 0.09 wt % phosphorus,0.4 wt % of sulphur and 1.0 wt % sulphated ash, based on the totalweight of the composition, comprising an oil of lubricating viscosityand being substantially free of friction-modifier.

In a fourth further aspect, the present invention provides a combinationof an engine having a rotating tappet and a lubricating oil compositionhaving up to 0.09 wt % phosphorus, 0.4 wt % of sulphur and 1.0 wt %sulphated ash, based on the total weight of the composition, comprisingan oil of lubricating viscosity and being substantially free offriction-modifier.

In a fifth further aspect, the present invention provides the use of alubricating oil composition having up to 0.09 wt % phosphorus, 0.4 wt %of sulphur and 1.0 wt % sulphated ash, based on the total weight of thecomposition, comprising an oil of lubricating viscosity and beingsubstantially free of friction-modifier to pass the 650 hour VW RNTengine test (PV1473 Draft).

In a sixth further aspect, the present invention provides the use of alubricating oil composition according having up to 0.09 wt % phosphorus,0.4 wt % of sulphur and 1.0 wt % sulphated ash, based on the totalweight of the composition, comprising an oil of lubricating viscosityand being substantially free of friction-modifier to pass both the VW PV1451 FE test and the 650 hour VW RNT test (PV1473 Draft).

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of a section of a valve train of anengine, and

FIG. 2 is a schematic representation of the cam and tappet action of thevalve train section of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The engine of the present invention is an internal combustion engine,such as a passenger car motor vehicle engine. The engine may be aspark-ignited engine or a compression-ignited engine.

The oil of lubricating viscosity useful in the practice of the inventionmay have a viscosity from about 2 mm²/sec (centistokes) to about 40mm²/sec, especially from about 3 mm²/sec to about 20 mm²/sec, mostpreferably from about 5 mm²/sec to about 15 mm²/sec, as measured at 100°C.

Natural oils include animal oils and vegetable oils (e.g., castor oil,lard oil); liquid petroleum oils and hydrorefined, solvent-treated oracid-treated mineral oils of the paraffinic, naphthenic and mixedparaffinic-naphthenic types. Oils of lubricating viscosity derived fromcoal or shale also serve as useful base oils.

Synthetic lubricating oils include hydrocarbon oils and halo-substitutedhydrocarbon oils such as polymerized and interpolymerized olefins (e.g.,polybutylenes, polypropylenes, propylene-isobutylene copolymers,chlorinated polybutylenes, poly(1-hexenes), poly(1-octenes),poly(1-decenes)); alkylbenzenes (e.g., dodecylbenzenes,tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)benzenes);polyphenyls (e.g., biphenyls, terphenyls, alkylated polyphenols); andalkylated diphenyl ethers and alkylated diphenyl sulfides andderivative, analogs and homologs thereof.

Alkylene oxide polymers and interpolymers and derivatives thereof wherethe terminal hydroxyl groups have been modified by esterification,etherification, etc., constitute another class of known syntheticlubricating oils. These are exemplified by polyoxyalkylene polymersprepared by polymerization of ethylene oxide or propylene oxide, and thealkyl and aryl ethers of polyoxyalkylene polymers (e.g.,methyl-polyiso-propylene glycol ether having a molecular weight of 1000or diphenyl ether of poly-ethylene glycol having a molecular weight of1000 to 1500); and mono- and polycarboxylic esters thereof, for example,the acetic acid esters, mixed C₃-C₈ fatty acid esters and C₁₃ Oxo aciddiester of tetraethylene glycol.

Another suitable class of synthetic lubricating oils comprises theesters of dicarboxylic acids (e.g., phthalic acid, succinic acid, alkylsuccinic acids and alkenyl succinic acids, maleic acid, azelaic acid,suberic acid, sebasic acid, fumaric acid, adipic acid, linoleic aciddimer, malonic acid, alkylmalonic acids, alkenyl malonic acids) with avariety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecylalcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycolmonoether, propylene glycol). Specific examples of such esters includesdibutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctylsebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate,didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyl diester oflinoleic acid dimer, and the complex ester formed by reacting one moleof sebacic acid with two moles of tetraethylene glycol and two moles of2-ethylhexanoic acid.

Esters useful as synthetic oils also include those made from C₅ to C₁₂monocarboxylic acids and polyols and polyol esters such as neopentylglycol, trimethylolpropane, pentaerythritol, dipentaerythritol andtripentaerythritol.

Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy- orpolyaryloxysilicone oils and silicate oils comprise another useful classof synthetic lubricants; such oils include tetraethyl silicate,tetraisopropyl silicate, tetra-(2-ethylhexyl)silicate,tetra-(4-methyl-2-ethylhexyl)silicate, tetra-(p-tert-butyl-phenyl)silicate, hexa-(4-methyl-2-ethylhexyl)disiloxane, poly(methyl)siloxanesand poly(methylphenyl)siloxanes. Other synthetic lubricating oilsinclude liquid esters of phosphorous-containing acids (e.g., tricresylphosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid)and polymeric tetrahydrofurans.

Other examples of base oil are gas-to-liquid (“GTL”) base oils, i.e. thebase oil may be oil derived from Fischer-Tropsch-synthesisedhydrocarbons made from synthesis gas containing hydrogen and carbonmonoxide using a Fischer-Tropsch catalyst. These hydrocarbons typicallyrequire further processing in order to be useful as base oil. Forexample, they may, by methods known in the art, be hydroisomerized;hydrocracked and hydroisomerized; dewaxed; or hydroisomerized anddewaxed.

Definitions for the base stocks and base oils in this invention are thesame as those found in the American Petroleum Institute (API)publication 1509 “Engine Oil Licensing and Certification System”,Fifteenth Edition, April 2002, Appendix E, November 2004. Saidpublication categorizes base stocks as follows:

-   a) Group I base stocks contain less than 90 percent saturates and/or    greater than 0.03 wt % sulphur and have a viscosity index greater    than or equal to 80 and less than 120 using the test methods    specified in Table 1.-   b) Group II base stocks contain greater than or equal to 90 percent    saturates and less than or equal to 0.03 wt % sulphur and have a    viscosity index greater than or equal to 80 and less than 120 using    the test methods specified in Table 1.-   c) Group III base stocks contain greater than or equal to 90 percent    saturates and less than or equal to 0.03 wt % sulphur and have a    viscosity index greater than or equal to 120 using the test methods    specified in Table 1.-   d) Group IV base stocks are polyalphaolefins (PAO).

e) Group V base stocks include all other base stocks not included inGroup I, II, III, or IV. TABLE 1 Analytical Methods for Base StockProperty Test Method Saturates ASTM D 2007 Viscosity Index ASTM D 2270Sulphur ASTM D 2622 ASTM D 4294 ASTM D 4927 ASTM D1552 ASTM D 3120

The oil of lubricating viscosity of the present invention may comprise aGroup I, Group II, Group III, Group IV or Group V base stock or base oilblends of the aforementioned base stocks.

Preferably, an oil of lubricating viscosity of the present inventioncomprises a proportion at least of one or more Group IV basestock.Suitably, a lubricating oil composition according to the presentinvention comprises at least 25 wt %, preferably at least 35 wt % andmore preferably at least 40 wt % of a Group IV base stock, based on thetotal weight of the composition. Suitably, a lubricating oil compositionaccording to the present invention comprises less than 85 wt %,preferably less than 75 wt %, more preferably less than 60 wt % andespecially less than 55 wt % of a Group IV base stock, based on thetotal weight of the composition.

Preferably, an oil of lubricating viscosity according to the presentinvention comprises a proportion at least of one or more Group IIIbasestock. Suitably, a lubricating oil composition according to thepresent invention comprises at least 15 wt %, preferably at least 20 wt% and more preferably, at least 25 wt % Group III basestock, based onthe total weight of the composition. Suitably, a lubricating oilcomposition according to the present invention comprises less than 80 wt%, preferably less than 60 wt % and, most preferably, less than 50 wt %of Group III basestock, based on the total weight of the composition.

A lubricating composition according to the present invention maycomprise one or more Group V ester base stock. Suitably, the lubricatingcomposition comprises less than 25 wt %, preferably less than 10 wt %and more preferably 5 wt % or less of an ester base stock based on thetotal weight of the composition. Suitably, a lubricating oil compositionaccording to the present invention comprises at least 1 wt %, preferablyat least 1.5 wt % and more preferably at least 3 wt % of an esterbasestock.

It should be noted that any of the basestocks mentioned above may beprovided to the composition as a separate component for blending.Alternatively, all or a proportion of any of the basestocks may beprovided to the composition as a diluent for another component of thelubricating oil composition.

It should be noted that substantially free of friction modifier isdefined herein as meaning the lubricating oil composition comprises lessthan 0.1 wt %, suitably less than 0.05 wt % (e.g., 0 to 0.4 wt %),preferably less than 0.01 wt %, such as 0 to 0.0075 wt % and mostpreferable no (0 wt %) friction modifier.

By friction modifier it is meant boundary lubricant additives that lowerfriction coefficients and hence improve fuel economy and includes, butis not necessarily limited to the following types of compounds.

(1) Organic, ashless (metal-free), nitrogen-free organic frictionmodifiers include esters formed by reacting carboxylic acids andanhydrides with alkanols. Such friction modifiers include, aliphaticcarboxylic acids, aliphatic carboxylic esters of polyols, such asglycerol esters of fatty acids, for example, glycerol oleate, boricasters of glycerol fatty acid monoesters, esters of long chainpolycarboxylic acids with diols, for example, the butane diol ester of adimerized unsaturated fatty acid, aliphatic phosphonates, aliphaticphosphates, aliphatic thiophosphates, aliphatic thiophosphonates,aliphatic thiophosphates and oxazoline compounds. The aliphatic groupusually contains at least eight carbon atoms so as to render thecompound suitably oil soluble. Esters of carboxylic acids and anhydrideswith alkanols are described in U.S. Pat. No. 4,702,850. Examples ofother conventional organic friction modifiers are described by M. Belzerin the “Journal of Tribology” (1992), Vol. 114, pp. 675-682 and M.Belzer and S. Jahanmir in “Lubrication Science” (1988), Vol. 1, pp.3-26.

(2) Ashless aminic friction modifiers include oil-soluble aliphaticeamines, alkoxylated mono- and di-amines and aliphatic fatty acidsamindes. One common class of such metal free, nitrogen-containingfriction modifier comprises ethoxylated amines. These amines may, forexample, be in the form of an adduct or reaction product with a boroncompound such as a boric oxide, boron halide, metaborate, boric acid ora mono-, di- or tri-alkyl borate. Other aminic friction modifiersinclude, alkoxylated alkyl-substituted mono-amines, diamines and alkylether amines, for example, ethoxylated tallow amine and ethoxylatedtallow ether amine and aliphatic carboxylic ester-amides. Examples offatty acid esters and amides as friction modifiers are disclosed in U.S.Pat. No. 3,933,659.

(3) Additives which deposit molybdenum disulfide. Such molybdenumcompounds include sulphur-containing, organo-molybdenum compounds, suchas, dithiocarbamates, dithiophosphates, dithiophosphinates, xanthates,thioxanthates, alkylthioxanthates and sulfides. Such molybdenumcompounds also include acidic molybdenum compounds that react with basicnitrogen as measured by ASTM test D-664 or D-2896 titration procedureand are typically hexavalent. Such compounds include molybdic acid,ammonium molybdate, sodium molybdate, potassium molybdate, and otheralkaline earth metal molybdates and other molybdenum salts, e.g.,hydrogen sodium molybdate, MoOCl₄, MoO₂Br₂, Mo₂O₃Cl₆, molybdenumtrioxide and similar molybdenum compounds.

A lubricating oil composition according to the present inventionsuitably comprises less than 1.0 wt % sulphated ash, preferably, lessthan 0.9 wt %, more preferably less than 0.8 wt % and particularly lessthan 0.7 wt % sulphated ash, based on the total weight of thecomposition. Advantageously, a lubricating oil composition according tothe present invention comprises 0.6 wt % or less sulphated ash measuredusing ASTM D874.

A lubricating oil composition according to the present inventionsuitably comprises less than 0.09 wt %, preferably less than 0.08 wt %and more preferably less than 0.07 wt % phosphorus, based on the totalweight of the composition. Advantageously, a lubricating oil compositionaccording to the present invention comprises 0.06 wt % of lessphosphorus, based on the total weight of the composition, measured usingASTM D4951.

A lubricating oil composition according to the present inventionsuitably comprises less than 0.4 wt %, preferably less than 0.3 wt % andmore preferably less than 0.2 wt % sulphur, based on the total weight ofthe composition, as measured using ASTM 5185 or ASTM 2622.

A lubricating oil composition according to the present inventionsuitably has a total base number (TBN) of 13 or less, preferably lessthan 10 and more preferably between 4 and 9, as measured using ASTMD2986.

A lubricating oil composition according to the present invention maycomprise additional conventional additives. Examples of suitableadditional additives are set out in the following pages.

Metal-containing or ash-forming detergents function as both detergentsto reduce or remove deposits and as acid neutralizers or rustinhibitors, thereby reducing wear and corrosion and extending enginelife. Detergents generally comprise a polar head with a long hydrophobictail. The polar head comprises a metal salt of an acidic organiccompound. The salts may contain a substantially stoichiometric amount ofthe metal in which case they are usually described as normal or neutralsalts, and would typically have a total base number or TBN (as can bemeasured by ASTM D2896) of from 0 to 80. A large amount of a metal basemay be incorporated by reacting excess metal compound (e.g., an oxide orhydroxide) with an acidic gas (e.g., carbon dioxide). The resultingoverbased detergent comprises neutralized detergent as the outer layerof a metal base (e.g. carbonate) micelle. Such overbased detergents mayhave a TBN of 150 or greater, and typically will have a TBN of from 250to 450 or more.

Detergents that may be used in a lubricating oil composition accordingto the present invention include oil-soluble neutral and overbasedsulfonates, phenates, sulphurized phenates, thiophosphonates,salicylates, and naphthenates and other oil-soluble carboxylates of ametal, particularly the alkali or alkaline earth metals, e.g., barium,sodium, potassium, lithium, calcium, and magnesium. The most commonlyused metals are calcium and magnesium, which may both be present, andmixtures of calcium and/or magnesium with sodium. Particularlyconvenient metal detergents are neutral and overbased calcium ormagnesium sulfonates having TBN of from 20 to 450, neutral and overbasedcalcium or magnesium phenates and sulphurized phenates having TBN offrom 50 to 450 and neutral and overbased magnesium or calciumsalicylates having a TBN of from 20 to 450. Combinations of detergents,whether overbased or neutral or both, may be used. Detergents generallyuseful in the formulation of lubricating oil compositions also include“hybrid” detergents formed with mixed surfactant systems, e.g.,phenate/salicylates, sulfonate/phenates, sulfonate/salicylates,sulfonates/phenates/salicylates, as described, for example, in U.S. Pat.Nos. 6,153,565; 6,281,179; 6,429,178; and 6,429,179.

The detergent may be present in any suitable amount, within the limitsprovided by the maximum sulphated ash and sulphur levels of thelubricating oil composition of the present invention. A detergent may beused in an amount providing the lubricating oil composition with fromabout 0.05 to about 0.30 wt %, such as from about 0.07 to about 0.25 wt%, more preferably from about 0.8 to about 0.22 wt % of calcium,measured as sulfated ash (SASH) content.

Ashless dispersants comprise an oil soluble polymeric hydrocarbonbackbone bearing one or more functional groups that are capable ofassociating with particles to be dispersed. Typically, the polymerbackbone is functionalized by amine, alcohol, amide, or ester polarmoieties, often via a bridging group. The ashless dispersant may be, forexample, selected from oil soluble salts, esters, amino-esters, amides,imides, and oxazolines of long chain hydrocarbon substituted mono anddicarboxylic acids or their anhydrides; thiocarboxylate derivatives oflong chain hydrocarbons; long chain aliphatic hydrocarbons having apolyamine attached directly thereto; and Mannich condensation productsformed by condensing a long chain substituted phenol with formaldehydeand polyalkylene polyamine.

The oil soluble polymeric hydrocarbon backbone of these dispersants istypically derived from an olefin polymer or polyene, especially polymerscomprising a major molar amount (i.e., greater than 50 mole %) of a C₂to C₁₈ olefin (e.g., ethylene, propylene, butylene, isobutylene,pentene, octene-1, styrene), and typically a C₂ to C₅ olefin. The oilsoluble polymeric hydrocarbon backbone may be a homopolymer (e.g.,polypropylene or polyisobutylene) or a copolymer of two or more of sucholefins (e.g., copolymers of ethylene and an alpha-olefin such aspropylene or butylene, or copolymers of two different alpha-olefins).Other copolymers include those in which a minor molar amount of thecopolymer monomers, for example, 1 to 10 mole %, is an α,ω-diene, suchas a C₃ to C₂₂ non-conjugated diolefin (for example, a copolymer ofisobutylene and butadiene, or a copolymer of ethylene, propylene and1,4-hexadiene or 5-ethylidene-2-norbornene). Preferred arepolyisobutenyl (Mn 400-2500, preferably 950-2200) succinimidedispersants. Preferably, a lubricating oil composition according to thepresent invention comprises from 0.005 to 0.08 wt %, preferably from0.01 to 0.08 wt %, most, preferably from about 0.05 to 0.08 wt % oftotal nitrogen. Suitably, substantially all of the nitrogen in thelubricating oil composition is provided by the dispersant.

A lubricating oil composition according to the present invention, maycomprise one or more borated dispersant. Such dispersants can be boratedby conventional means, as generally taught in U.S. Pat. Nos. 3,087,936;3,254,025 and 5,430,105. Boration of the dispersant is readilyaccomplished by treating an acyl nitrogen-containing dispersant with aboron compound such as boron oxide, boron halide boron acids, and estersof boron acids, in an amount sufficient to provide from about 0.1 toabout 20 atomic proportions of boron for each mole of acylated nitrogencomposition. Preferably, lubricating oil compositions of the presentinvention contain less than 100 ppm of boron, such as less than 90 ppmof boron, more preferably, less than 80 ppm, such as less than 70 ppm ofboron.

Dihydrocarbyl dithiophosphate metal salts are frequently used asantiwear and antioxidant agents. The metal may be an alkali or alkalineearth metal, or aluminum, lead, tin, molybdenum, manganese, nickel orcopper. The zinc salts are most commonly used in lubricating oil inamounts of 0.1 to 10 wt %, preferably 0.2 to 2 wt %, based upon thetotal weight of the lubricating oil composition. They may be prepared inaccordance with known techniques by first forming a dihydrocarbyldithiophosphoric acid (DDPA), usually by reaction of one or more alcoholor a phenol with P₂S₅ and then neutralizing the formed DDPA with a zinccompound. For example, a dithiophosphoric acid may be made by reactingmixtures of primary and secondary alcohols. Alternatively, multipledithiophosphoric acids can be prepared where the hydrocarbyl groups onone are entirely secondary in character and the hydrocarbyl groups onthe others are entirely primary in character. To make the zinc salt, anybasic or neutral zinc compound could be used but the oxides, hydroxidesand carbonates are most generally employed. Commercial additivesfrequently contain an excess of zinc due to the use of an excess of thebasic zinc compound in the neutralization reaction.

The preferred zinc dihydrocarbyl dithiophosphates are oil soluble saltsof dihydrocarbyl dithiophosphoric acids and may be represented by thefollowing formula:

wherein R and R′ may be the same or different hydrocarbyl radicalscontaining from 1 to 18, preferably 2 to 12, carbon atoms and includingradicals such as alkyl, alkenyl, aryl, arylalkyl, alkaryl andcycloaliphatic radicals. Particularly preferred as R and R′ groups arealkyl groups of 2 to 8 carbon atoms. Thus, the radicals may, forexample, be ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl,amyl, n-hexyl, i-hexyl, n-octyl, decyl, dodecyl, octadecyl,2-ethylhexyl, phenyl, butylphenyl, cyclohexyl, methylcyclopentyl,propenyl, butenyl. In order to obtain oil solubility, the total numberof carbon atoms (i.e. R and R′) in the dithiophosphoric acid willgenerally be about 5 or greater. The zinc dihydrocarbyl dithiophosphate(ZDDP) can therefore comprise zinc dialkyl dithiophosphates. Althoughthe lubricating oil compositions of the present invention are capable ofproviding excellent performance in the presence of amounts of ZDDPproviding greater amounts of phosphorus, the improved performance of theinventive lubricating oil compositions are particularly apparent inlower SAPS formulations, which generally have phosphorous levels of nogreater than about 0.08 wt % (800 ppm). Therefore, lubricating oilcompositions of the present invention suitably contain less than 800ppm, preferably less than 700 ppm and more preferably 600 ppm or less ofphosphorus. Lubricating oil compositions according to the presentinvention suitably comprise at least 50 ppm, preferably at least 100 ppmand more preferably at least 200 ppm of phosphorus.

Oxidation inhibitors or antioxidants reduce the tendency of mineral oilsto deteriorate in service. Oxidative deterioration can be evidenced bysludge in the lubricant, varnish-like deposits on the metal surfaces,and by viscosity growth. Such oxidation inhibitors include hinderedphenols, alkaline earth metal salts of alkylphenolthioesters havingpreferably C₅ to C₁₂ alkyl side chains, calcium nonylphenol sulfide, oilsoluble phenates and sulphurized phenates, phosphosulphurized orsulphurized hydrocarbons or esters, phosphorous esters, ashless andmetal-containing thiocarbamates, and oil soluble copper compounds asdescribed in U.S. Pat. No. 4,867,890.

Aromatic amines having at least two aromatic groups attached directly tothe nitrogen constitute another class of compounds that is frequentlyused for antioxidancy. Typical oil soluble aromatic amines having atleast two aromatic groups attached directly to one amine nitrogencontain from 6 to 16 carbon atoms. The amines may contain more than twoaromatic groups. Compounds having a total of at least three aromaticgroups in which two aromatic groups are linked by a covalent bond or byan atom or group (e.g., an oxygen or sulphur atom, or a —CO—, —SO₂— oralkylene group) and two are directly attached to one amine nitrogen alsoconsidered aromatic amines having at least two aromatic groups attacheddirectly to the nitrogen. The aromatic rings are typically substitutedby one or more substituents selected from alkyl, cycloalkyl, alkoxy,aryloxy, acyl, acylamino, hydroxy, and nitro groups. The amount of anysuch oil soluble aromatic amines having at least two aromatic groupsattached directly to one amine nitrogen should preferably not exceed 0.4wt % active ingredient.

Preferably, lubricating oil compositions in accordance with the presentinvention contain from about 0.05 to about 5 wt %, preferably from about0.10 to about 3 wt %, most preferably from about 0.20 to about 2.5 wt %of phenolic antioxidant, aminic antioxidant, or a combination thereof,based on the total weight of the lubricating oil composition.

Lubricating oil compositions according to the present invention mayoptionally comprise a rust or corrosion inhibitor. Any suitable rust orcorrosion inhibitor may be used. As rust inhibitors there may bementioned nonionic polyoxyalkylene polyols and esters thereof,polyoxyalkylene phenols and anionic alkyl sulfonic acids. Preferably, alubricating oil composition according to the present invention comprisesa succinic acid based rust inhibitor and/or an alkyl substituted phenolethoxylate.

As copper and lead bearing corrosion inhibitors there may be mentionedthe thiadiazole polysulfides containing from 5 to 50 carbon atoms, theirderivatives and polymers thereof. Such materials are widely known anddisclosed, for example, in U.S. Pat. No. 2,719,125, U.S. Pat. No.4,097,387 and GB Patent No. 1 560 830.

If present the rust or corrosion inhibitor is suitably present in anamount not exceeding 1.0 wt %, and preferably not exceeding 0.5 wt %,based on the total weight of the composition.

Foam control can be provided by an antifoamant of the polysiloxane type,for example, silicone oil or polydimethyl siloxane.

In the present invention it may be advantageous to include an additivethat maintains the stability of the viscosity of the blend. Additiveswhich are effective in controlling this viscosity increase include thelong chain hydrocarbons functionalized by reaction with mono- ordicarboxylic acids or anhydrides which are used in the preparation ofthe ashless dispersants as hereinbefore disclosed. In another preferredembodiment, the lubricating oil compositions of the present inventioncontain an effective amount of a long chain hydrocarbons functionalizedby reaction with mono- or dicarboxylic acids or anhydrides (e.g.,polyisobutenyl succinic anhydride (PIBSA)).

The viscosity index of the base stock may be increased, or improved, byincorporating therein certain polymeric materials that function asviscosity modifiers (VM) or viscosity index improvers (VII). Generally,polymeric materials useful as viscosity modifiers are those havingnumber average molecular weights (Mn) of from about 5,000 to about250,000, preferably from about 15,000 to about 200,000, more preferablyfrom about 20,000 to about 150,000. Polymer molecular weight,specifically Mn, can be determined by various known techniques. Oneconvenient method is gel permeation chromatography (GPC), whichadditionally provides molecular weight distribution information (see W.W. Yau, J. J. Kirkland and D. D. Bly, “Modern Size Exclusion LiquidChromatography”, John Wiley and Sons, New York, 1979). Another usefulmethod for determining molecular weight, particularly for lowermolecular weight polymers, is vapor pressure osmometry (see, e.g., ASTMD3592).

A viscosity index improver dispersant functions both as a viscosityindex improver and as a dispersant. Examples of viscosity index improverdispersants include reaction products of amines, for example polyamines,with a hydrocarbyl-substituted mono -or dicarboxylic acid in which thehydrocarbyl substituent comprises a chain of sufficient length to impartviscosity index improving properties to the compounds. In general, theviscosity index improver dispersant may be, for example, a polymer of aC₄ to C₂₄ unsaturated ester of vinyl alcohol or a C₃ to C₁₀ unsaturatedmono-carboxylic acid or a C₄ to C₁₀ di-carboxylic acid with anunsaturated nitrogen-containing monomer having 4 to 20 carbon atoms; apolymer of a C₂ to C₂₀ olefin with an unsaturated C₃ to C₁₀ mono- ordi-carboxylic acid neutralised with an amine, hydroxyamine or analcohol; or a polymer of ethylene with a C₃ to C₂₀ olefin furtherreacted either by grafting a C₄ to C₂₀ unsaturated nitrogen-containingmonomer thereon or by grafting an unsaturated acid onto the polymerbackbone and then reacting carboxylic acid groups of the grafted acidwith an amine, hydroxy amine or alcohol. A preferred lubricating oilcomposition contains a dispersant composition of the present invention,base oil, and a viscosity index improver dispersant.

Pour point depressants (PPD), otherwise known as lube oil flow improvers(LOFIs) lower the temperature. Typical additives that improve the lowtemperature fluidity of the fluid are C₈ to C₁₈ dialkyl fumarate/vinylacetate copolymers, and polymethacrylates Like VM, LOFIs can be graftedwith grafting materials such as, for example, maleic anhydride, and thegrafted material can be reacted with, for example, amines, amides,nitrogen-containing heterocyclic compounds or alcohol, to formmultifunctional additives.

Some other of the above-mentioned additives can also provide amultiplicity of effects; thus for example, a single additive may act asa dispersant-oxidation inhibitor. This approach is well known and neednot be further elaborated herein.

When lubricating compositions contain one or more of the above-mentionedadditives, each additive is typically blended into the base oil in anamount that enables the additive to provide its desired function.Representative effective amounts of such additives, when used incrankcase lubricants, are listed below. ADDITIVE WT % (Broad) WT %(Preferred) Dispersant 0.1-20  1-8 Metal Detergents 0.1-15 0.2-9 Corrosion Inhibitor  0-5   0-1.5 Metal Dihydrocarbyl Dithiophosphate0.1-6  0.1-4  Antioxidant  0-5 0.01-2.5 Pour Point Depressant 0.01-5 0.01-1.5 Antifoaming Agent  0-5 0.001-0.15 Supplemental Antiwear Agents 0-1.0   0-0.5 Viscosity Modifier 0.01-10  0.25-3  

It may be desirable, although not essential to prepare one or moreadditive concentrates comprising additives (concentrates sometimes beingreferred to as additive packages) whereby several additives can be addedsimultaneously to the oil to form the lubricating oil composition.

The final composition may employ from 5 to 30 wt %, preferably 5 to 25wt %, typically 10 to 20 wt % of the concentrate, the remainder beingoil of lubricating viscosity.

The terms “oil-soluble” or “dispersible” used herein do not necessarilyindicate that the compounds or additives are soluble, dissolvable,miscible, or capable of being suspended in the oil in all proportions.These do mean, however, that they are, for instance, soluble or stablydispersible in oil to an extent sufficient to exert their intendedeffect in the environment in which the oil is employed. Moreover, theadditional incorporation of other additives may also permitincorporation of higher levels of a particular additive, if desired.

Throughout this specification reference to quantitative amounts of acomponent are given on an active ingredient basis. It is common for someadditives to be combined with a diluent.

The present invention advantageously provides a method of reducing wearof the rotating tappets in passenger car motor vehicles engineslubricated with lower SAPS lubricants.

It is unexpected that removal of conventional friction modifieradditives from the lubricating oil used to lubricate an enginecomprising a rotating tappet would provide an improvement in wearperformance, particularly of the rotating tappet. It is particularlysurprising that the present invention also exhibits acceptable fueleconomy performance despite the absence of friction modifier, which isnormally thought necessary for acceptable fuel economy performance.

The invention will be further described, by way of example only, withreference to FIG. 1 and FIG. 2.

FIG. 1, shows part of an engine valve train comprising a rotating tappet6. It can be seen from FIG. 1 that a cam lobe 2, supported on camshaft4, contacts the end face of the rotating tappet 6, which is connected tothe valve 10.

In use, the cam lobe 2 is rotated by rotation of the cam shaft 4 onwhich it is mounted. There is a point of contact between the cam lobe 2and the face of the rotating tappet 6. The action of the eccentric shapecam effects linear reciprocating motion of the tappet 6. In moving tothe distal extreme of this linear reciprocating motion (not shown) thetappet 6 actuates the valve 10 and compresses the valve spring 8. As thecamshaft 4 continues to rotate and the cam lobe 2 releases the tappet 6,the tappet moves back to the proximate extreme of this linear motion (asillustrated in FIG. 1) by relaxation of the valve spring the valve 10closes.

During operation of the engine at operating temperature and oilpressure, the cam surface, of which the cam lobe 2 is part, remains incontinuous contact with the face of the tappet 6. As shown in FIG. 2,the point of contact between the cam 2 and tappet 6 is off-set from theaxis of linear reciprocating motion by distance X. Consequently inaddition to the linear reciprocating motion, the rotational motion ofthe camshaft 4 also translates into rotational motion of the tappet 6about the axis of linear motion. This motion is clearly illustrated inFIG. 2.

As the cam lobe 2 rotates there is a sliding contact between the surfaceof the cam lobe 2 and the face of the tappet 6. The rotational movementof the tappet 6 means that the point of contact between cam lobe 2 andtappet 6 varies. Thus any mechanical stress, deformation or wear of thetappet 6 by the impact of the cam lobe 2 is evenly distributed over theworking face of the tappet 6, rather then being concentrated within afixed or restricted area.

The present invention advantageously facilitates rotation of the tappetand reduces stalling of the tappet, thus effecting improved wearperformance.

This invention will be further understood by reference to the followingexamples, which include preferred embodiments of the invention.Compositions described as “comprising” a plurality of defined componentsare to be construed as including compositions formed by admixing theplurality of defined components.

EXAMPLES Example 1

The VW RNT test (Draft PV 1473) is one test used to evaluate cam andtappet wear. The test uses a 1.91 TDI PD, 85 kW VW diesel engine on astatic engine bench test. This engine has a rotating tappet and camdesign. The test is a continuous test of 650 hour duration. Prior to thetest the exhaust cam and tappet (number 1) are irradiated and the wearis monitored on-line using a radio nucleide tracer technique.

Four oils were blended and tested in the 650 hour VW RNT test (PV1473Draft). Oils 1 and 2 are lubricating oil compositions in accordance withthe present invention, and comprise no friction modifier. Oils A and Bare comparative examples and comprise glycerol monooleate and oleamidefriction modifiers.

Each of oils 1, 2, A and B had a sulphated ash content of 0.6 wt %, aphosphorus content of 0.06 wt % and a sulphur content of around 0.22 wt%. Each of the exemplified oils was blended to a viscosity grade of5W-30, according to SAE J300 May 2004.

The test results are set out below in Table 2. TABLE 2 Measure Oil 1 Oil2 Oil A Oil B Radiated Cam Wear (nm) 2182 1157 12006 4296 RadiatedTappet Wear (nm) 4194 1375  8957 8479 Radiated cam and tappet Pass PassFail Fail (Cam Limit = 4000) (Tappet Limit = 5000)

The above results demonstrate that the lubricants containing no frictionmodifier performed better in the 650 hour VW RNT test (PV 1473 Draft)than comparable formulations with friction modifier, showing reducedwear on the rotating tappet. In fact, Oils 1 and 2 in accordance withthe present invention passed the test as defined by the radiated cam andtappet limit, whereas the comparative Oils A and B failed.

It is unexpected that removal of a friction modifier from a passengercar motor vehicle lubricating oil composition would provide improvedwear resistance of the rotating tappet.

Example 2

The VW PV 1451 FE test measures fuel economy. It involves comparison ofcandidate oils against a specified reference oil (CEC RL 191).

Oil 2, as above, and Oil C were tested in the VW FE PV1451 test. Oil Ccorresponds essentially with Oil B of example 1, except that Oil Ccontained only glycerol monooleate friction modifier. Each of Oils 2 andC and reference oil CEC RL 191 were run in the test and the fuel savingof Oils 2 and C was measured relative to the reference oil.

The test results are set out in Table 3 below. TABLE 3 Measure Oil 2 OilC Fuel savings (%) 2.03 2.04 Result (Pass ≧2.0%) Pass Pass

It can be seen from Table 3 that both Oils 2 and C pass the VW PV P1451FE test for fuel economy. It can therefore be seen that a lubricatingoil according to the present invention not only passes the 650 hour VWRNT test (PV 1473 Draft), but also passes the VW PV 1451 FE test, andthus provides a combination of acceptable wear resistance and fueleconomy. It is unexpected that a lubricating oil composition for apassenger car motor vehicle being substantially free of frictionmodifier would pass both industry wear and fuel economy tests. This isparticularly unexpected in a lower SAPS oil composition, which isinherently limited as to the amount of metal dihydrocarbyldithiophosphate anti-wear additive that can be used in the composition.

1. A method of lubricating an internal combustion engine having a camand a rotating tappet, the method comprising employing as the lubricantfor the engine a lubricating composition comprising a base oil oflubricating viscosity, phosphorus in an amount of from 50 to 900 ppm bymass, sulfur in an amount of from 1500 to 3000 ppm by mass, boron in anamount of from 0.0 to 100 ppm, sulphated ash in an amount not exceeding1.0 mass %, and friction modifier in an amount of from 0.0 to 0.1 mass%, said amounts being based on the mass of fully formulated lubricatingoil composition.
 2. The method of claim 1 wherein the lubricating oilcomposition comprises less than 0.05 mass % friction modifier, based onthe mass of fully formulated oil composition.
 3. The method of claim 1,wherein any friction modifier in the lubricating compositions isselected from one or more of the following: glycerol esters of fattyacids, nitrogen-containing friction modifiers and molybdenum compounds.4. The method of claim 1, wherein sulphated ash of the lubricating oilcomposition amounts to less than 0.7 mass %.
 5. The method of claim 1,wherein the phosphorus content of the lubricating oil composition is0.06 mass % or less, based on the mass of the fully formulatedcomposition.
 6. The method of claim 1, wherein the boron content of thecomposition is less than 90 ppm by mass.
 7. The method of claim 1,wherein the lubricating oil composition comprises one or more additivesselected from: metal-containing or ash-forming detergents; ashlessdispersants; borated ashless dispersants; dihydrocarbyl dithiophosphatemetal salts as antiwear and antioxidant agents; oxidation inhibitors orantioxidants; rust or corrosion inhibitors; foam control agents;viscosity stabilizing agents; viscosity modifying agents; pour pointdepressants; and supplemental antiwear agents.
 8. The method of claim 1,wherein the lubricating oil composition comprises one or morenitrogen-containing dispersants, which dispersant(s) provide saidcomposition with from 0.005 to 0.08 mass % of nitrogen.
 9. An internalcombustion engine having a rotating tappet lubricated with a lubricatingoil composition comprising a base oil of lubricating viscosity;phosphorus in an amount of from 50 to 90 ppm by mass; sulfur in anamount of from 1500 to 3000 ppm by mass; boron in an amount of from 0.0to 0.1 mass %, sulphated ash in an amount not exceeding 1.0 mass %; andfriction modifier in an amount of from 0.0 to 0.1 mass %, said amountsbeing based on the mass of fully formulated lubricating oil composition.